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Memory utilization on AIX systems typically runs around 100%. This is often a source of concern. However, high memory utilization in AIX does not imply the system is out of memory. By design, AIX leaves files it has accessed in memory. This significantly improves performance when AIX reaccesses these files because they can be reread directly from memory, not disk*. When AIX needs memory, it discards files using a "least used" algorithm. This generates no I/O and has almost no performance impact under normal circumstances.
Sustained paging activity is the best indication of low memory. Paging activity can be monitored using the "vmstat" command. If the "page-in" (PI) and "page-out" (PO) columns show non-zero values over "long" periods of time, then the system is short on memory. (All systems will show occasional paging, which is not a concern.)
Memory requirements for applications can be empirically determined using the AIX "rmss"command. The "rmss" command is a test tool that dynamically reduces usable memory. The onset of paging indicates an application's minimum memory requirement.
Finally, the "svmon" command can be used to list how much memory is used each process. The interpretation of the svmon output requires some expertise. See the AIX documentation for details.
The vmo parameters also needs to be tuned

Like the previous reply mentioned, it is normal for physical memory to be near 100% even with almost nothing running. If you watch it after a reboot you will see it gradually creep up to just about 100%. It might take a matter of minutes or a matter of days depending on what is running. I know it doesn't take Oracle long to fill it up.

There is no need to worry until it starts using a lot of paging space, mine is usually less than 1% even with Oracle running. I usually use nmon to do a quick check of everything.

HI,
i would sugest you that u increase the paging size in the system as
it is a general practise that we keep the paging size double the actual
memory in the system,now as u have upgraded the memory create a paging space
of equal sizes but on different hdisk ,that will distribute the i/o load
equally and also increase performance
Regards
Bhushan...

On Wed, Jan 6, 2010 at 6:06 AM, Shak via ibm-aix-l <
email@removed wrote:
> Posted by Shak(Senior technical specialist)
> on Jan 6 at 6:09 AM
>
> Memory utilization on AIX systems typically runs around 100%. This is often
> a source of concern. However, high memory utilization in AIX does not imply
> the system is out of memory. By design, AIX leaves files it has accessed in
> memory. This significantly improves performance when AIX reaccesses these
> files because they can be reread directly from memory, not disk*. When AIX
> needs memory, it discards files using a "least used" algorithm. This
> generates no I/O and has almost no performance impact under normal
> circumstances.
> Sustained paging activity is the best indication of low memory. Paging
> activity can be monitored using the "vmstat" command. If the "page-in" (PI)
> and "page-out" (PO) columns show non-zero values over "long" periods of
> time, then the system is short on memory. (All systems will show occasional
> paging, which is not a concern.)
> Memory requirements for applications can be empirically determined using
> the AIX "rmss"command. The "rmss" command is a test tool that dynamically
> reduces usable memory. The onset of paging indicates an application's
> minimum memory requirement.
> Finally, the "svmon" command can be used to list how much memory is used
> each process. The interpretation of the svmon output requires some
> expertise. See the AIX documentation for details.
> The vmo parameters also needs to be tuned
>

I see no reason to have double the paging space as you do memory, especially if it is not using much paging space. On my Oracle box I actually have a little less paging space than I have memory and have had no problems. Before I upgraded my memory I used to have 1 and 1/2 times the memory in paging space and paging was about 40%, now it is less than 1%

I must agree with Larry here. If you have many GB of physical RAM there
is little or no need for swap. If your machine uses a lot of swap then
you should really think about tuning the system and then adding more
memory again if swap is still excessive.

The whole purpose of swap was to provide a means to prevent a machine
from halting through running out of memory from the days when memory was
extremely expensive and machines had only a few MB's of RAM.

These days machines have GBs of RAM and therefor you shouldn't need more
than 2-4GB of swap (any more than this then performance is impacted
through disk seek times when accesing virtual memory that has been
fragmented on the swap volume).

I suspect that the reason why you can see high memory utilisation will
be due to the OS using the free space as a cache. These settings can be
tuned through minperm and maxperm vmo settings, but I don't personally
know enough to recommend actual settings in your scenario.

Thank you everyone !!
I m agree with larry n warwick that increasing paging space can't be a
solution for this problem as paging space utilization is minimal on this
server.
I've gone thru some documents n read abt file buffer cache which depends on
"maxclient%" . Currently it is 90%. If I reduce it to 50%, can it help
to release some pages in memeory ?

Avinash, you are approaching this the wrong way. What is the actual problem that the application is experiencing? Or is it running ok? Did you have a performance problem at 16GB that you expected to be fixed by increasing to 32GB? Examining metrics in isolation of the problem will tell you very little about the system. Think about your own body. If you measure the temperature it is 37C. Is that hot? Well it is hotter than most places on earth but it happens to be the correct temperature for a human being, so there is no problem. Indeed there is an acceptable range in body temperatures. One only worries about it if one is also feeling ill - then you measure temperature.

Thanx for the reply sjm...
I have never mentioned that there is any problem with application or system
performance. What made me curious in this issue is the unknown utilization
of memory. I just wanted to get more information and nothing is wrong in
gaining more knowledge.
In the past we have faced lot of problems due to high memory utilization. So
precaution is better than cure.
If you can explain unknown utilization of memory...I'll really appreciate ur
efforts !!!

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